Conventional hydraulic systems, for example, those implemented in mobile handling machines such as large excavators, forego the opportunity to recover energy from the fluid for regeneration through the system. For example, when pressurized fluid passes through a control valve to tank, energy is converted to heat in the hydraulic fluid. The heat must then be removed by supplying operational energy to a cooling system, such as a radiator and fan. Additionally, heating and re-heating of hydraulic fluids to undesirable temperatures has an adverse affect on the performance of the fluids.
Some conventional hydraulic systems include an energy recovery facility. For example, the mobile working machine described in International Publication No. WO 00/00748 has a hydraulic circuit that includes an energy recovery facility. The hydraulic circuit may recover lowering load energy from hydraulic fluid by way of a pump/motor in communication with an accumulator. However, the hydraulic circuit can only recover energy from the head end of an actuator, and in some circumstances the machine drive unit must supply operational energy to the pump/motor in order to recover the lowering load energy.
A fluid control system for reducing the energy requirement of a hydraulic circuit and for effectively and efficiently providing energy recovery capability to a hydraulic circuit is desired. The present invention is directed to solving one or more of the problems set forth above.